public class Change {
    public  static void mul(int[] arr){
        for (int i = 0; i < arr.length; i++) {
            arr[i] *= 2;
        }
    }
    public static void main(String[] args) {
        int[] arr = {1,2,3,4};
        for (int i = 0; i < arr.length; i++) {
            System.out.print(arr[i] + " ");
        }
        mul(arr);
        System.out.println();
        for (int i = 0; i < arr.length; i++) {
            System.out.print(arr[i] + " ");
        };
    }
}
